Engine/Transmission (1998.5 - 2002) Sluggish Smoky Acceleration

[Vaughn MacKenzie]

My '98. 5 started acting odd about 10 days ago, started when I removed and cleaned and reinstalled the injectors. This is a stock truck. Went from spunky to a dog and MPG has taken a dive. Rolling into the throttle for moderate acceleration the first 2-3psi boost starts to build and then it's slow to reach 10psi. Then around 10 it suddenly gets a good surge of power and shoots up to its normal limit of 20psi. Below 10psi when you're giving it some throttle there's a steady stream of black smoke and EGTs are a good 200F on the hot side, easily runs to 600-700 with fairly mild acceleration. As soon as the surge of power comes on the smoke completely disappears, even when it's 100 degrees out, and EGTs don't increase.



Thinking the huge crack in the exhaust manifold was the cause I replaced it, but it didn't help at all. I thought reusing the exhaust gaskets was allowing exhaust leaks but putting new ones on made little difference. Next I figured the turbo was toast so I put the one off my '96 on it, helped slightly. I went all over the intake system and couldn't find any place there could be a boost leak, pretty sure that's not the cause because big boost leaks let boost start up pretty quick and then fall off fast, which is the opposite what I have.



The only other thing I can think of it's the IAT or MAP sensor. . . that's the next try, stay tuned.

 

[NIsaacs]

What was the reason for the injector cleaning? Was it doing this before? If it was fine before, than it kinda points to the injector clean up. It is always hard to make suggestions to good mechanics, like you are, but if you are like me, sometimes you can't see the forest for the trees



Nick

 

[cerberusiam]

Try cleaning the MAP sensor with electrical component spray cleaner, or replace it. Sounds like the MAP has a dead spot in it.

 

[Vaughn MacKenzie]

I finally got around to cleaning both sensors yesterday, they were somewhat dirty especially the IAT, but it didn't have a noticeable effect. The truck is pretty much a dud below 10psi boost, just doesn't have the spunk it used to. It's pretty anemic on the freeway, if you're rolling along at 70 and give it some throttle the response is very weak. . . if I want to have decent acceleration I have to drop OD and rap it out.

It is also pretty temperature sensitive, in the mornings when it's in the low 70s it's halfway decent, in the afternoons between 90-100 degrees it's a real dud.

I really doubt the injectors are the issue, it idles way too smooth and also once it hits 10psi it takes off good and no smoke at all running WOT. I cleaned the injector tips (external cleaning only) for the heck of it, they really had a bunch of deposits.

This is the 4th 24V I have owned, every one was stock at one point, never had one do this or act weak like this in stock form.

 

[cerberusiam]

It is also pretty temperature sensitive, in the mornings when it's in the low 70s it's halfway decent, in the afternoons between 90-100 degrees it's a real dud.

If it started right after the injector removal, and, given the above, the cross over tubes are a likely suspect. Not TQ'ed right, crushed too far, maybe pitted or a small scratch.

 

[Vaughn MacKenzie]

I'm planning to swap new injectors in with new tubes in the next couple of weeks. The engine was built Jan '98 so it has the old ones.

 

[Vaughn MacKenzie]

As an update I have since installed a tubular exhaust header and Garrett GT3788 ball bearing turbo with 4" exhaust, and a van Aaken box. Also put in new MAP and IAT sensors. Runs quite a bit better but part of it is the van Aaken masks the problem, EGT soars and it still puffs black smoke when boost is in the 3-10psi range trying to accelerate. So latest thought is there is something up with the injection pump in that the advance piston must be sticking. I really doubt it's an injector or cross tube issue, runs too smooth and doesn't have any fuel leaks. I'm going to try and scare up a good used VP44 instead of dropping coin on a new one especially since I'm not sure it's the problem.

 

[JR]

Does it start hard? How about codes? Are you by chance sucking air into your fuel lines anywhere? When you hit this "doggy" period does it feel like a dead pedal or does the rpm jump around like its coming in and out?

 

[Vaughn MacKenzie]

Starts normal, don't think it's sucking air. I've had dead pedal before but that's not what it's doing. RPM doesn't jump around.
I don't know if it's throwing codes, I have a 98 so I would need a scan tool to look them up which I'm going to try and do.

 

[Vaughn MacKenzie]

Well problem solved! Replacing the injectors and injector tubes cleared the annoying smoke and it runs great. I put in a new set of Stage I Edge Jammers from Source Automotive, good for roughly 50-60hp. Not sure if something happened when I wire-brushed the tips of the stockers or reusing the early non-reusable injector tubes was the culprit, but glad this one's solved. I just installed them today. It was hot yesterday and it was really smoking.